select
    p.port_code as 港コード,
    p.port_name as 港名,
    sub.入国者数,
    sub.出国者数,
    sub.入国者数 - sub.出国者数 as 差分
from
    port p
    join (
        select
            i.port_code,
            sum(
                case
                    when i.kind_code = '110' and g.group_code = '120' then i.amt
                    else 0
                end
            ) as 入国者数,
            sum(
                case
                    when i.kind_code = '120' and g.group_code = '120' then i.amt
                    else 0
                end
            ) as 出国者数
        from
            immigration i
            join grp g on g.group_code = i.group_code
        group by
            i.port_code
    ) as sub on sub.port_code = p.port_code
where
    sub.入国者数 - sub.出国者数 > 0
order by
    差分 desc,
    p.port_code desc